Lignocellulosic biomass is abundant and can provide a sustainable resource for producing fuels, chemicals and biobased materials. The hemicellulose and cellulose content of the biomass can be converted to pentose and hexose sugars by acid hydrolysis with lignin as a residue. By performing the acid hydrolysis in two stages at different temperatures the total yield of sugars can be increased compared to a one-stage process. In such a process the first stage is a milder treatment targeting the hemicellulose part which is easier to hydrolyze compared to the cellulose. In the second reactor stage more severe conditions are applied to break down the cellulose into sugars. If the process would be run using one reactor unit, the liberated hemicellulose sugars would decompose further and create unwanted by-products. Hence, it is beneficial to run the hydrolysis process in two reactor units instead of one unit. Conventionally, enzymatic hydrolysis is applied after a pretreatment stage to convert lignocellulosic biomass into sugars. Such conversion processes are associated with high operating costs due to the consumption of expensive enzymes.
When the process is run in two stages a solid-liquid separation is needed between the two reactor units to remove the hemicellulose sugars prior to the second reactor unit. Conventional equipment for separation of liquid from fibrous biomass, e.g., filters and presses, operate at atmospheric pressure. This entails that the pressure has to be reduced between the two reactor units to the atmospheric pressure from the pressure of the first reactor stage in order to perform the washing and this, in turn, means that the biomass material has to be reheated to the desired temperature in the second reactor or in a pre-heating unit before entering the second reactor.
This pressure reduction and pressure increase between the reactor units is energy demanding and also time consuming. Therefore, there is a need within the biorefining industry of improved arrangements for feeding and dewatering partly hydrolyzed material between reactor units in a system for a hydrolysis process and for removing hemicellulose and hemicellulose-derived sugars from the material in the two-stage hydrolysis process.
In EP 2 247 781 a two-stage system for pre-treatment of cellulosic biomass material is presented. The pre-treatment, which includes a steam explosion stage, prepares the biomass for the following enzymatic hydrolysis stage for liberation of the sugars.
However, there is still a need in the industry for improved systems and arrangements for feeding and dewatering partly hydrolyzed material in two-stage processes.